1. Field of the Invention
This invention relates to intumesced coatings and more particularly to intumesced closed cell coatings for pipe.
2. Description of the Prior Art
The term sodium silicate denotes a compound represented by the formula Na.sub.2 O.(SiO.sub.2).sub.n.xH.sub.2 O wherein n is any number from 1-5 and x is the number 1 or larger. Foamed (intumesced) products formed from sodium silicate are known in the art, e.g., see U.S. Pat. No. 3,741,898 and U.S. Pat. No. 3,951,834. These foam products are used as structural and insulation materials. The products' resistance to high temperature and moisture together with low thermal conductivity and excellent mechanical strength makes them especially suited for insulation. In addition, foam ceramics and shaped articles are formed from aqueous mixtures containing alkali metal silicates, which on heating to a temperature between 700.degree.-1100.degree. C., form a sintered porous mass. More particularly, sodium silicate, which is known as waterglass, has been known to produce porous products by heating aqueous mixtures containing such waterglass and mineral granules of different types. Further, cementitious materials can be added to alkali silicates to impart mechanical strength to alkali silicate foam bodies such as is disclosed in U.S. Pat. No. 4,084,980. These cementitious materials include materials consisting predominantly of at least one compound selected from the group consisting of oxides and composite oxides of alkali earth metals. Such cementitious materials include calcium silicate, Portland cement, alumina cement, lime alumina cement, lime slag cement, magnesium silicate and the like.
In another aspect of the invention, lances for use in the production of steel are subject to thermal and chemical degradation during use. Typically these lances are immersed in molten metal and slag and oxygen is delivered through the lance and into the molten metal at temperatures of about 3000.degree. F. Since the lances are immersed in the molten metal and/or slag and the lances themselves are typically manufactured of metal, the lances are slowly consumed during the steelmaking process. One way of reducing the consumption of the lances is by jacketing the lances and providing water cooling to reduce consumability. However, this method of retarding consumption of the lances is expensive and dangerous due to the violent physical and chemical reaction if the cooling jacket bursts admitting water into the molten metal. Thus it has been desired in the steel industry to provide a lance which is protected from the heat given off by the molten metal in order to reduce lance consumption in the steelmaking process.
In the production of aluminum, flux wands are used to introduce gases such as CO, Cl.sub.2, and N.sub.2 into the molten aluminum bath. In order to avoid reaction of these gases and, more particularly, Cl.sub.2, wands having linings and coatings of a ceramic material are used. These wands are expensive and the ceramic coating is fragile tending to chip and delaminate thus causing holes in the wand and making the wand useless for feeding the gas to the desired location in the aluminum bath.
In accordance with the present invention, an intumesced closed cell silicate is provided which adheres to steel and is particularly adaptable for use as a coating on steelmaking lances, aluminum flux wands and pipe.